Electrophotographic composition and element

ABSTRACT

4-AMINOBENZO(B)PYRYLIUM AND 4-AMINOBENZO(B)THIAPYRYLIUM SALTS ARE SENSITIZERS FOR ORGANO-METALLIC PHOTOCONDUCTORS. PHOTOCONDUCTIVE COMPOSITIONS SENSITIZED WITH THESE COMPOUNDS HAVE INCREASED ELECTROPHOTOGRAPHIC SPEED AND ARE SENSITIVE IN THE ULTRAVIOLET REGION OF THE SPECTRUM.

United States Patent U.S. Cl. 961.6 Claims ABSTRACT OF THE DISCLOSURE 4-aminobenzo [b] pyrylium and 4 aminobenzo[b]thiapyrylium salts are sensitizers for organo-metallic photoconductors. Photoconductive compositions sensitized with these compounds have increased electrophotographic speed and are sensitive in the ultraviolet region of the spectrum.

This is a continuation-in-part of U.S. application Ser. No. 754,499, filed Aug. 21, 1968.

This invention relates to the novel use of a class of organic compounds as sensitizers in electrophotographic elements.

The process of xerography, as disclosed by Carlson in U.S. Pat. No. 2,297,691, employs an electrophotographic element comprising a support material bearing a coating of a normally insulating material whose electrical resistance varies with the amount of incident actinic radiation it receives during an imagewise exposure. The element, commonly termed a photoconductive element, is first given a uniform surface charge after a suitable period of dark adaptation. The element is then exposed to a pattern of actinic radiation which has the effect of differentially reducing the potential of the surface charge in accordance with the relative energy contained in various parts of the radiation pattern. The differential surface charge or electrostatic latent image remaining on the electrophotographic element is then made visible by contacting the surface with a suitable electroscopic marking material. Such marking material or toner, whether contained in an insulating liquid or on a dry carrier, can be deposited on the exposed surface in accordance with either the charge pattern or in the absence of charge pattern as desired. The deposited marking material may then be either permanently fixed to the surface of the sensitive element by known means such as heat, pressure, solvent vapor and the like or transferred to a second element to which it may similarly be fixed. Likewise, the electrostatic latent image can be transferred to a second element and developed there.

Various photoconductive insulating materials have been employed in the manufacture of electrophotographic elements. For example, vapors of selenium and vapors of selenium alloys deposited on a suitable support and particles of photoconductive zinc oxide held in a resinous, film-forming binder have found wide application in present-day document copying applications.

Since the introduction of electrophotography, a great many organic compounds have been found to possess some degree of photoconductivity. Many organic compounds have revealed a useful level of photoconduction and have been incorporated into photoconductive compositions. In addition, many organo-metallic photoconductive compounds have been found to be very useful. Optically clear organo-metallic photoconductor-containing elements having desirable electrophotographic properties can be especially useful in electrophotography. Such ice electrophotographic elements may be exposed through a transparent base, if desired, thereby providing unusual flexibility in equipment design. Such compositions when coated as a film or layer on a suitable support also yield an element which is reusable; that is, it can be used to form subsequent images after residual toner from prior images has been removed by transfer and/ or cleaning.

Although some of the various photoconductor materials referred to above are inherently light sensitive, their degree of sensitivity is usually low and not always in a desired wavelength portion of the spectrum so that it is common practice to add materials to increase the speed and to shift the spectral sensitivity.

Increasing the speed and shifting the sensitivity of such systems has several advantages in that it reduces exposure time, allows projection printing through various optical systems etc. By increasing the speed through the use of sensitizers, photoconductors which would otherwise have been unsatisfactory are useful in processes where higher speeds are required. However, a major disadvantage of many of the prior sensitized photoconductor systems has been the highly colored nature of such systems.

It is, therefore, an object of this invention to provide a novel class of sensitizers for use in combination with organo-metallic photoconductors.

Another object of this invention is to provide novel sensitized photoconductive elements.

A further object of this invention is to provide novel photoconductive compositions which are colorless and are sensitive to ultraviolet radiation.

These and other objects are accomplished by the use of 4-arninobenzo[b]pyrylium and 4-aminobenzo[b]thiapyrylium salts as sensitizers in organo-metallic photo conductor-containing systems. Typical sensitizers of the present invention include those having the following structural formula:

wherein:

X is a sulfur atom or an oxygen atom;

Z is an anionic function including such acid anions as perchlorate, fluoroborate, sulfonate, periodate, p-toluenesulfonate etc.

R is an alkyl radical typically having 1 to 10 carbon atoms, such as methyl, ethyl, isopropyl, n-butyl, pentyl, octyl, decyl etc. including cycloalkyl such as cyclopentyl, cyclohexyl etc., as well as such substituted alkyl radicals as aralkyl radicals typically having 1 to 4 carbon atoms in the alkyl moiety such as benzyl, phenylethyl, phenylpropyl and phenylbutyl; an aryl radical such as phenyl and naphthyl radicals; and the like;

R is a hydrogen atom, a lower alkyl radical typical ly having 1 to 4 carbOn atoms such as methyl, ethyl, isopropyl, butyl etc. and a lower alkoxy radical typically having 1 to 4 carbon atoms in the alkyl moiety such as methoxy, ethoxy, propoxy, butoxy etc.; and

R and R when taken separately each represents a hydrogen atom and when taken together are attached to adjacent carbon atoms and represent the atoms necessary to form a fused aromatic ring such as a benzo ring and including substituted fused aromatic rings.

Suitable sensitizers would include the following representative compounds:

TABLE A (c) an aryl radical including substituted aryl radicals such as aminoaryl, alkylaryl and haloaryl,

Name

Number:

4-benzylamino-2-pheny1benzolblpyrylium perchlorate.

4-ani1ino-2-(4-methoxyphenyl)naphtho[l,2-b]pyrylium perchlorate. l-(N -butylamluo)-3-phenylnaphtho[2,1-b1pyryliu1n perchlorate. 4-(N-butylamluo)-2-(4-methoxyphenyl)naphtho-[l,2-b]-pyrylium perchlorate. 5 1-anilino-3-phenylnaphtho[2,1-b1pyrylium perchlorate. 6. 4-(N-butylamino)-2-phenylbenzo[b]thiapyryliu.m perchlorate.

4-am'lino fiavylium perchlorate.

Electrophotographic elements of the invention can be prepared with a variety of organo-metallic photoconductive compounds and the sensitizing compounds of this invention in the usual manner, i.e., by blending a dispersion or solution of the photoconductive compound together with an electrically insulating, film-forming resin binder when necessary or desirable and coating or forming a self-supporting layer with the photoconductive composition. Generally, a suitable amount of the sensitizing compound is mixed with the photoconductive coating composition so that after thorough mixing the sensitizing compound is uniformly distributed throughout the desired layer of the coated element. The amount of sensitizer that can be added to a photoconductor-containing layer to give effective increases in speed can vary widely. The optimum concentration in any given case will vary with the specific photoconductor and sensitizing compound used. In general, substantial speed gains can be obtained where an appropriate sensitizer is added in a concentration range from about 0.0001 to about 30 percent by weight based on the weight of the film forming coating composition. Normally, a sensitizer is added to the coating composition in an amount from about 0.005 to about 5.0 percent by weight of the total coating composition.

The sensitizers of this invention are effective for enhancing the electrophotosensitivity of a wide variety of organometallic photoconductors. The photoconductors used are thse organo-metallic compounds which exhibit an electrophotosensitivity to light and are capable of forming transparent elements. A class of organo-metallic photoconductors which are particularly well suited for use with the present sensitizers includes organo-metallic compounds which are the organic derivatives of Group IHa, lVa or Va metals such as those having at least one aminoaryl group attached to the metal atom and as described in copending Johnson US. patent application Ser. No. 755,711, filed Aug. 27, 1968 and Goldman and Johnson, US. patent application Ser. No. 650,664, filed July 3, 1967.

The metallic substituents of these organo-metallic photoconductors are Group I-IIa, Group IVa or Group Va metals in accordance with the Periodic Table of the Elements (Handbook of Chemistry and Physics, 38th edition, pp. 394-95) and include boron, aluminum, gallium, indium, and thallium from Group IIIa, silicon, germanium, tin and lead from Group IVa and phosphorus, arsenic, antimony and bismuth from Group Va. The organo-metallic photoconductors useful in this invention can be substituted on the metal nucleus with a wide variety of substitutents but at least one of the substituents must be an aminoaryl radical. The amino radical can be positioned anywhere on the aromatic nucleus, but best results are obtained if the aryl moiety is a phenyl radical having the amino group in the 4 or para position. Typical substituents attached to the metal nucleus include the following:

(a) a halogen, sulfur or oxygen atom,

(b) an alkyl radical, including substituted alkyl radicals,

(d) an oxygen-containing radical such as an alkoxy or aryloxy radical,

(e) an amino radical including substituted amino radicals such as mono and diarylamino and monoand dialkyl amino radicals,

(f) a heterocyclic radical, and

(g) a Group IIIa, IVa or Va organo metallic radical.

Illustrative photoconductors of this invention are represented by the following structures:

(a) a hydrogen atom;

(b) an aryl radical including substituted and unsubstituted aryl radicals such as a phenyl radical, a naphthyl radical, a dialkylaminophenyl radical, etc.;

(0) an alkyl radical having 1 to 8 carbon atoms;

((1) an alkoxy radical having 1 to 8 carbon atoms;

(e) an aryloxy radical such as a phenoxy radical;

(f) an amino radical having the formula wherein R and R can be hydrogen atoms or alkyl radicals having 1 to 8 carbon atoms; or

(g) a heterocyclic radical having 5 to 6 atoms in the hetero nucleus including at least one nitrogen atom such as a triazolyl, a pyridyl radical, etc.;

E, G, L and Q and in addition can be a Group IVa organo-metallic radical, or when taken with B, an oxygen atom or a sulfur atom;

I can be any of the substituents set forth above for E, G, L and Q, and when taken with E, an oxygen atom or a sulfur atom.

Some typical organo-metallic photoconductors of this invention include the compounds listed below:

carbonates; poly(ethyleneglycol-co-bishydroxyphenyl propane terephthalate); nuclear substituted polyvinyl haloarylates; etc. Methods of making resins of this type have been described in the prior art, for example, styrene-alkyd resins can be prepared according to the method described in US. Pats. 2,361,019 and 2,258,423. Suitable resins of the type contemplated for use in the photoconductive layers of the invention are sold under such trade names Name Triphenyl-pdiethylaminophenylsilane.

Methyl-diphenyl-p-diethylaminophenylsilane. Triphenyl-p-diethylaminophenylgermane.

Triphenyl p-dimethylaminophenylstannane.

- Triphenyl-p-diethylaminophenylstannane.

.. Diphenyl-bis-(p-diethylaminophenyl)stannane.

. Triphenyl-p-diethylarninophenylplumbane.

Tetra-p-diethylaminophenylplumbane.

Tetra-p-diethylaminophenylgermane.

- Phenyl-bis-(p-diethylaminophenyl)phosphine. Bis(p-diethylaminophenyl) phosphine oxide. Tris-p-dimethylaminophenylarsine. Trls-p-diethylaminophenylarsine. 2-methyl-4dimethylaminophenylarsine oxide. Tris-p-diethylaminophenylbismuthine. Methyl-bis(p-diethylaminophenyl)arsine. Methyl-bis-(p-diethylaminophenyl)phosphine. Diphenyl-p-diethylaminophenylsilane. p-Diethylaminophenylarsine.

4,4 ,4"-tris (diethylamino) tetraphenylstannane.

Tris-(p-diethylaminophenyl) phosphine sulfide. Bis-(p-diethylaminophenyl)thioxostannane. Bis[2-mesityl-4-(N-piperidmo)phenyHborane.

Tri-p-diethylarninophenylborane. Tri-p-diphenylaminophenylborane. Tri-p-methylaminophenylgallium. Methyl-phenylp-diethylamlnophenylborane: 2-naphthyl-p-dimethylaminophenylborane. p-Dipropylaminophenylborane. Di-p-diethylaminophenylborane.

Diphenoxy-p-dibutylaminophenyl aluminum. Tri-(2,fi-dimethyl-4-diethylaminophenyl) indium; 2-chloro--dimethylaminophenyl gallium hydride.

Diphenylamino-p-diethylaminophenylborane. Dimesityl-4-dimethylaminonaphthylborane. Dimesityl-4-dimethylarninophenylborane. Dimesityl-(3,5-dimethyl-l-methoxyphenyl)borane Dimesityl-4-diphenylaminophenylbcrane. 1,2-bis(pdiethylaminophenyl)diborane.

62 l-phenyl-Z-methyldiborane.

Tri-(2,G-diphenoxy-4-diethylaminophenyl)thallium; Tri-(2,fi-dimethoxy-4-dirnethylaminophenyl) thallium.

Bis[2-mesityl-4-(N,N-dimethylamino)phenyl1borane;

Ethoxy-p-dimethylaminophenyl aluminum hydride:

Tetrakis-[diphenyl- (p-diethylaminophenyl) plumbyflmethane. Tetrakis-[diphenyl-(p-dlethylammophenyl)stannyHStannane. Bis-[phenyl-(p-dlethylaminophenyl)]dibismuthine.

The organo-metallic photoconductors useful in the present invention can generally be prepared by known methods. For example, the aminoaryl lead and tin compounds can be prepared in accordance with J. Am. Chem. Soc., 54, 3726-9 (1932) or J. Org. Chem., 15, 994(1950). The aminoaryl germanium compounds are made by the method set forth in Chem. Abstracts, 60, p, 395d. A method for making the aminoaryl bismuthines has been described by Gilman and Yablunky (J. Am. Chem. Soc., 63, 207-211 [1941]). Aminoaryl derivatives of arsenic are prepared in accordance [With J. Indian Chem. Soc., 16, 5 -518 (1939). Phosphorus and antimony compounds containing aminoaryl moieties may be prepared by methods described in Chem. Abstracts, 28-, 3392 and Chem. Abstracts, 46896, respectively.

Preferred binders for use in preparing the present photoconductive layers comprise polymers having fairly high dielectric strength which are good electrically insulating film-forming vehicles. Materials of this type comprise styrene-butadiene copolymers; silicone resin; styrenealkyd resins; silicone-alkyd resins; soya-alkyd resins; poly(vinyl chloride); poly(vinylidene chloride); vinylidene chloride-acrylonitrile copolymers; poly(vinyl acetate); vinyl acetate-vinyl chloride copolymers; poly(vinyl acetals), such as poly(vinyl butyral); polyacrylic and methacrylic esters, such as poly(methylmethacrylate), poly(nbutylmethacrylate), poly(isobutyl methacrylate), etc.; polystyrene, nitrated polystyrene; polymethylstyrene; isobutylene polymers; polyesters, such as poly(ethylene alkaryloxyalkylene terephthalate); phenol-formaldehyde resins; ketone resins; polyamide; polycarbonates; polythioas Vitel PE-101, Cymac, Piccopale 100, Saran F-220 and Lexan 105. Other types of binders which can be used in the photoconductive layers of the invention include such materials as paraflin, mineral waxes, etc.

Solvents of choice for preparing coating compositions of the present invention can include a number of solvents such as benzene, toluene, acetone, 2-butanone, chlorinated hydrocarbons, e.g., methylene chloride, ethylene chloride, etc., ethers, e.g., tetrahydrofuran, or mixtures of these solvents, etc.

In preparing the coating composition useful results are obtained Where the photoconductor substance is present in an amount equal to at least about 1 Weight percent of the coating composition. The upper limit in the amount of photoconductor substance present can be widely varied in accordance with usual practice. In those cases Where a binder is employed, it is normally required that the photoconductor substance be present in an amount from about 1 weight percent of the coating composition to about 99 weight percent of the coating composition. A preferred Weight range for the photoconductor substance in the coating composition is from about 10 weight percent to about 60 weight percent.

Coating thicknesses of the photoconductive composition on a support can vary widely. Normally, a coating in the range of about 0.001 inch to about 0.01 inch before drying is useful for the practice of this invention. The preferred range of coating thickness is found to be in the range from about 0.002 inch to about 0.006 inch before drying although useful results can be obtained outside of this range.

Suitable supporting materials for coating the photoconductive layers of the present invention can include any of a wide variety of electrically conducting supports, for example, paper (at a relative humidity above 20 percent); aluminum-paper laminates; metal foils such as aluminum foil, zinc foil, etc.; metal plates, such as aluminum, copper, zinc, brass and galvanized plates; vapor deposited metal layers such as silver, nickel, aluminum and the like coated on paper of conventional photographic film bases such as cellulose acetate, polystyrene, etc. Such conducting materials as nickel can be coated by vacuum deposition on transparent film supports in sufficiently thin layers to allow electrophotographic elements prepared therewith to be exposed from either side of such elements. An especially useful conducting support can be prepared by coating a support material such as poly(ethylene terephthalate) with a conducting layer containing a semiconductor dispersed in a resin. Such conducting layers both with and without insulating barrier layers are described in US. Pat. 3,245,833. Likewise, a suitable conducting coating can be prepared from the sodium salt of a carboxyester lactone of maleic anhydride and a vinyl acetate polymer. Such kinds of conducting layers and methods for their optimum preparation and use are disclosed in U.S. 3,007,901 and 3,267,807.

The elements of the present invention can be employed in any of the well-known electrophotographic processes which require photoconductive layers. One such process is the aforementioned xerographic process. As explained previously, in a process of this type the electrophotographic element is given a blanket electrostatic charge by placing the same under a corona discharge which serves to give a uniform charge to the surface of the photoconductive layer. This charge is retained on the layer by virtue of the substantial insulating property of the layer, i.e., the low conductivity of the layer in the dark. The electrostatic charge formed on the surface of the photoconducting layer is then selectively dissipated from the surface of the layer by exposure to light through an imagebearing transparency by a conventional exposure operation such as, for example, by contact-printing technique, or by lens projection of an image, etc., to form an electrostatic latent image in the photoconducting layer. By exposure of the surface in this manner, a charged pattern is created by virtue of the fact that light causes the charge to be conducted away in proportion to the intensity of the illumination in a particular area. The charge pattern remaining after exposure is then developed, i.e., rendered visible, by treatment with a medium comprising electrostatically attractable particles having optical density. The developing electrostatically attractable particles can be in the form of a dust or a pigment in a resinous carrier or a liquid developer can be used in which the developing particles are carried in an electrically insulating liquid carrier. Methods of development of this type are widely known and have been described in the patent literature in such patents, for example, as US. 2,297,691 and in Australian Pat. 212,315. In processes of electrophotographic reproduction such as in xerography, by selecting a developing particle which has a low-melting resin as one of its components, it is possible to treat the developed photoconductive material with heat and cause the powder to adhere permanently to the surface of the photoconductive layer. In other cases, a transfer of the image formed on the photoconductive layer can be made to a second support which would then become the final print. Techniques of the type indicated are Well known in the art and have been described in a number of US. and foreign patents such as US. Pats. 2,297,691 and 2,551,582 and in RCA Review, vol. 15 (1954), pages 469-484.

An increasing use of electrophotographic elements has occurred in the field of recording data displayed on a cathode-ray tube. Advantages gained through such use include attractively high photographic speed, desirable 8 spectral response, and short time f access to a visible recorded image.

It is frequently desirable to employ the image-bearing electrophotographic element having a transparent film base as a master from which further prints can be generated. Such elements can be used as masters in many types of reproduction processes. Typical of these processes are the xerographic process, thermographic process, direct electrostatic process, stabilization process, gelatin transfer process, diffusion transfer process, etc. A particularly advantageous process by which such a print can be made is the diazo process. In this process, a diazonium salt-containing element is exposed through a transparent electrophotographic original bearing a developed or toned image to activating radiation from an ultraviolet source. The exposure causes decomposition of the salt in those areas which are struck by activating radiation. Subsequently, the exposed diazo element is passed through an atmosphere of a suitable alkaline material, such as ammonia vapor. In the presence of the alkaline material and a dye-forming coupler, which can 'be either incorporated in the diazoniumcontaining layer or introduced during the development step, the diazonium salt which is not decomposed by exposure is converted to an azo dye. A positive reproduction of the original is formed.

A difliculty commonly encountered in the production of copies from sensitized photoconductor-containing coated elements is that the photoconductive element possesses a relatively high optical opacity resulting from coloration irnparted by the sensitized photoconductor-containing composition. As a result the element does not transmit sufficient radiation in that portion of the electromagnetic spectrum to which the copy element is sensitive. Therefore, reprints are very difficult to obtain. Also, if the imagebearing elements are to be used for direct reading, the image portions of the elements are often almost indiscernible due to the lack of contrast. One solution proposed for this problem has been to bleach the highly colored photoconductive element. However, with the present class of sensitizers, a colorless photoconductive layer results which eliminates the need for an extra bleaching step.

The photoconductive compositions of the present invention are particularly sensitive in the ultraviolet region of the spectrum. Because of this short wavelength sensitivity, the standard test procedures for compositions sensitive in the visible region of the spectrum are not particularly meaningful when testing the present composition. One of the major reasons for not using standard test procedures is that they usually involve exposure to a 3000 K. tungsten light source. A light source of this nature is relatively deficient in ultraviolet radiation and thus such a test procedure would not adequately measure the unique characteristic of the present compositions. Accordingly, the speed of the photoconductive compositions according to the present invention are best shown when measured in terms of the time required to photodecay, upon exposure to an ultraviolet source, from an initial surface potential, V0, to some lower predetermined surface potential V. This photodecay test is described further in Example 1. Of course, some increase in speed can be seen even when measurement is made using a tungsten source and standard test procedures as described further in Example 4.

The following examples are included for a further understanding of the invention.

EXAMPLE 1 A control coating is prepared from the following ingredients 1.5 g. polycarbonate resin formed from the reaction between phosgene and a dihydroxydiarylalk-ane or from the ester exchange reaction between diphenylcarbonate and 2,2-bis-(4hydroxyphenyl)propane (binder) 0.5 g. 4,4',4"-tris(diethylamino)tetraphenyl tin (photoconductor) 11.7 ml. methylene chloride (solvent) 9 The above homogeneous photoconductive composition is coated at a wet thickness of 0.004 inch onto a poly(ethy1- ene terephthala-te) film support carrying a conductive layer of the sodium salt of a polymeric lactone as described in US. Pat. No. 3,260,706. During the coating step, the coating block temperature is maintained at 90 F. The resultant electrophotographic element is called Element 1 (control). The above procedure is then repeated with the addition of 0.01 g. 4-(N-butylamino)-2-(4-methoxyphenyl)benzo[b]pyrylium perchlorate as a sensitizer in the photoconductive compositions. The resultant element is colorless and is designated Element 2. Next, the two elements are measured for speed in a photodecay test as follows. The elements are electrostatically charged positively or negatively under a corona source until the surface potential, as measured by an electrometer probe, reaches about 600 volts. The charged elements are then exposed with a 365 my line exposure. Atfter exposure,the time required for the surface charge to decay to a value of 100 volts is noted. The relative response of each element is then expressed in terms of the time (in seconds) required for the element to photodecay from 600 to 100 volts. This time measurement is referred to as the positive or negative 100 volt photodecay time. The decay times of the elements are recorded in Table I below.

TABLE I 100 volt photodecay time, seconds Element number Positive Negative These elements can then be charged, imagewise exposed and developed with a liquid developer of the type described in US. Pat. No. 2,907,674 to form visible images.

EXAMPLE 2 Three electrophotographic elements are prepared by the general procedure of Example 1 using 1.5 g. of poly (vinyl-m-bromobenzoate-co-vinylacetate) as the binder, 0.5 g. of tetra-p-diethylaminophenylgermane as the photoconductor, 11.7 ml. of solvent and varying amounts of the sensitizer 4-(N-butylamino)-2-(4 methoxyphenyl)benzo [b]pyrylium perchlorate. Elements 3, 4 and 5 contain 1, 2 and 3 weight percent, respectively. The elements are then charged to +600 volts as in the previous example. The charged elements are then exposed to a xenon light source through a 1.9 neutral density filter in combination with a set of filters simulating the Wavelength distributi n of the emission spectrum of a P-16 phosphor. A P-16 phosphor is a standard phosphor used in cathode ray tubes. This phosphor fluoresces in the ultraviolet to blue spectral region with an emission peak at 3800 A. The l l6 phosphor is comprised of calcium magnesium sillcate doped with cesium. After exposure, the times required for the surface charge to decay to 100 and to 50 volts are noted. The relative response of each element is then expressed in terms of the time (in seconds) required for the element to photodecay from 600 to 100 volts and to 50 volts. These decay time measurements are shown in Table II below.

As in Example 1, these elements can be charged, imagewise exposed and developed with a suitable developer to form visible images.

10 EXAMPLE 3 Four electrophotographic elements are prepared as in the previous examples. The binder used in all the elements is the same as in Example 2. Element 6 contains tetra-pdiethyl-aminophenylplumbane as the photoconductor with no sensitizer. Element 7 contains the same photoconductor as Element 6 with 1% by weight of 4- (N-butylamino)- 2-(4-methxyphenyl)benzo[b]pyrylium perchlorate as the sensitizer. Element 8 contains 4,4'-bis-(diethylamino)triphenylarsine as the photoconductor with no sensitizer. Element 9 contains the same photoconductor as Element 8 with 1% of the sensitizer of Element 7. The elements are then charged, exposed and measured for their positive and negative volt photodecay times as in Example 1. These measurements are shown in Table III below.

As in the preceding examples, these elements can be charged, imagewise exposed and developed to form visible images.

EXAMPLE 4 Four electrophotographic elements are prepared by the general procedure of Example 1 using 1.5 g. of poly (vinyl-m-bromobenzoate-co-vinylacetate) as the binder in each, 0.5 g. of 4,4'-bis (diethylamino)triphenylarsine as the photoconductor in elements 10 and 11, 0.5 g. of 4,4',4"-tris(diethylamino)tetraphenylstannane as the conductor in elements 12 and 13, varying amounts of 4-(N- butylamino) -2- (4-methoxyphenyl benzo [b] pyrylium perchlorate as in the sensitizer in elements 10, 11 and 12 and 2% by weight of 4-cyclohexylamino-2-phenylbenzo [b] thiapyrylium perchlorate as the sensitizer in element 13. The resultant electrophotographic elements are then electrostatically charged under a corona source until the surface potential, as measured by an electrometer probe, reaches about 600 volts. The charged elements are then exposed to a 3000 K. tungsten light source through a stepped density gray scale. The exposure causes reduction ot the surface potential of the elements under each step of the gray scale from its initial potential, V0, to some lower potential, V, whose exact value depends on the actual amount of exposure in meter-'candle-seconds recevied by the area. The results of these measurements are then plotted on a graph of surface potential V vs. log exposure for each step. The actual positive or negative speed of the photoconductive composition used can then be expressed in terms of the reciprocal of the exposure required to reduce the surface potential to any fixed arbitrarily selected value. In this example, the actual positive or negative speed is the numerical expression of 10 divided by the exposure in meter-candle-seconds required to reduce the 600 volt charged surface potential to a value of 500 volts (100 volt shoulder speed) or to a value of 100 volts (100 volt toe speed). The speeds of the elements are recorded in Table IV below.

These elements can then be charged, exposed and developed with dry developers of the type described in U.S. Reissue Patent No. 25,136 to form visible images.

1 1 EXAMPLE 5 Five electrophotographic elements are prepared by the general procedure of Example 1 using 1.5 g. of the binder of Example 1, 0.5 g. of 4,4,4"-tris(diethylamino)tetraphenylstannane as the photoconductor and 0.1% by weight of the sensitizer shown in Table V below. The elements are charged, exposed and their positive and negative 100 volt shoulder speeds are measured as in Example 4. The results of these measurements are shown in Table V below.

[b]-thlapyrylium perchlorate.

These elements can then be charged, exposed and developed with dry developers of the type described in US. Reissue Patent No. 25,136 to form visible images.

EXAMPLE 6 Two electrophotographic elements are prepared by the general procedure of Example 1 using 1.5 g. of Vitel 101 as the binder and 0.375 g. of bis[2-mesityl-4-(N-piperidino)phenyl]borane as the photoconductor. The control element (No. 19) contains no sensitizer; whereas the other element (No. 20) contains 0.0375 g. of 4-(N-n-butylamino)-2-(4-methoxyphenyl)benzo [b] pyrilium perchlorate. Vitel 101 is a polymer obtained from Goodyear Tire & Rubber Co. and is a polyester of terephthalic acid and 2,2 bis[4 (,B-hydroxyethoxy)phenyl]propane in which the substituted propane is replaced in a 50:50 molar ratio with ethylene glycol. These two elements are charged, exposed and measured for positive and negative 100 v. shoulder speeds as in Example 4 only using an unfiltered xenon source. The results of these measurements are shown in Table VI below.

TABLE VI 100 volt shoulder speed Element Number Positive Negative 19 (control)- 250 63 20 630 250 The elements can be charged, imagewise exposed and developed as in the preceding examples to form a visible image.

EXAMPLE 7 TABLE VII 100 volt shoulder speed Element Number Positive Negative 21 (control)- 200 50 22 800 450 The elements thus formed can be charged, exposed and developed as in the preceding examples.

The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.

We claim:

1. A photoconductive composition comprising an organO-rnetallic photoconductor, an electrically insulating, film-forming resin binder and a sensitizing amount of a member selected from the group consisting of 4-aminobenzo[b]pyrylium and 4-aminobenzo[b]thiapyrylium salts, said photoconductor being selected from the group consisting of a Group IIIa organo-metallic compound having at least one aminoaryl radical attached to a Group IIIa metal, a Group No organo-metallic compound having at least one aminoaryl radical attached to a Group IVa metal and a Group Va organo-metallic compound having at least one aminoaryl radical attached to a Group Va metal.

2. A photoconductive composition as in claim 1 wherein the 4-aminobenzo[b]pyrylium and 4-aminobenzo[b] thiapyrylium salts have the formula:

wherein X is selected from the group consisting of a sulfur atom and an oxygen atom;

Z is an anion;

R is selected from the group consisting of an alkyl radical and an aryl radical;

R is selected from the group consisting of a hydrogen atom, a lower alkyl radical and a lower alkoxy radical; and

R and R when taken separately each represent a hydrogen atom and when taken together are attached to adjacent carbon atoms and represent the atoms necessary to form a fused aromatic ring.

3. A photoconductive composition as in claim 1 Wherein the 4-arninobenzo[b]pyryliurn and 4-aminobenzo[b] thiapyrylium salts are selected from the group consisting of:

4-.benzylamino-Z-phenylbenzo [b] pyrylium perchlorate,

4 anilino 2 (4 methoxyphenyl)naphtho[1,2-b]

pyrylium perchlorate,

1 (N-butylamino) 3 phenylnaphtho[2,l-b]pyrylium perchlorate,

4 (N butylamino) 2 (4 methoxyphenyl)naphtho- [1,2-b]pyrylium perchlorate,

1 anilino 3 phenylnaphtho[2,l-b]pyrylium perchlorate,

4 (N butylamino) 2 phenylbenzo [bJthiapyrylium perchlorate,

4-anilin0 flavylium perchlorate,

4 cyclohexylamino 2 phenylbenzo[b]thiapyrylium perchlorate,

4 (N octylamino) 2 phenylbenzo[b]thiapyrylium perchlorate,

4 phenylamino 2 phenylbenzo [b]thiapyryliurn perchlorate,

2 phenyl 4 phenethylaminobenzo[b]thiapyrylium perchlorate,

4 (N butylamino) 2 (p methoxyphenyl)benzo- [b] pyrylium fluoroborate,

13 a 4 (N butylamino) 2 (p methoxyphenyl)benzo- [b]pyrylium perchlorate, 4 (N n butylamino) 2 (4 methoxyphenyl) benzo[b]pyrylium fluoroborate, and 4 benzylamino 2 phenylbenzo [b] thiapyrylium perchlorate. 4. A photoconductive composition as in claim 1 wherein the organo-metallic photoconductor is selected from the group consisting of:

triphenyl-p-diethylaminophenylsilane,

methyl-diphenyl-p-diethylaminophenylsilane,

triphenyl-p-diethylaminophenylgermane, triphenyl-p-dimethylaminophenylstannane, triphenyl-p-diethylaminophenylstannane,

diphenyl-bis- (p-diethylaminophenyl) stannane,

triphenyl-p-diethylaminophenylplumbane,

tetra-p-diethylaminophenylplumbane,

tetra-p-diethylaminophenylgermane,

phenyl-bisp-diethylaminophenyl) pho sphine,

bis-(p-diethylaminophenyl) phosphine oxide,

tris-p-dimethylaminophenylarsine, tris-p-diethylaminophenylarsine,

Z-methyl-4-dimethylaminophenylarsine oxide,

tris-p-diethylaminophenylbismuthine,

methyl-bisp-diethylaminophenyl) arsine,

methyl-bis-(p-diethylaminophenyl)phosphine,

diphenyl-p-diethylaminophenylsilane, p-diethylarninophenylarsine,

4,4',4"-tris diethylamino tetraphenylstannane,

tetrakis [diphenyl (p diethylaminophenyl)plumbyl] methane,

terakis [diphenyl (p diethylaminophenyl)stannyl] stannane,

bis- [phenyl- (p-diethylaminophenyl) dibismuthine,

tris- (p-diethylaminophenyl) phosphine sulfide,

bisp-diethylaminophenyl) thioxostannane,

bis [2-mesityl-4- (N-piperidino) phenyl] borane,

bis[2 mesityl 4 (N,N dimethylamino)phenyl] borane,

tri-p-diethylaminophenylborane,

tri-p-diphenylaminophenylborane,

tri-p-methylaminophenylgallium, methyl-phenyl-p-diethylaminophenylborane, 2-naphthyl-p-dimethylaminophenylborane, p-dipropylaminophenylborane, di-p-diethylaminophenylborane, ethoxy-p-dimethylaminophenyl aluminum hydride, diphenoxy-p-dibutylaminophenyl aluminum,

tri- 2,6-dimethyl-4-diethylarninophenyl) indium,

2-chloro-4-dimethylaminophenyl gallium hydride,

tri- 2,6-diphenoxy-4-diethylaminophenyl thallium,

tri- (2,6-dimethoxy-4-dirnethylarninophenyl) thallium,

diphenylamino-p-diethylaminophenylborane,

di-mesityl-4-dimethylaminonaphthylborane, dimesityl-4-dimethylaminophenylborane,

dimesityl- (3 -dimethyl-4-methoxyphenyl) borane,

dimesityl-4-diphenylaminophenylborane, 1,2-bis (p-diethylaminophenyl) diborane, and

1-phenyl-2-methyldiborane.

5. An electrophotographic element comprising a support having coated thereon a layer of a photoconductive composition containing an organo-metallic photoconductor and a sensitizing amount of a member selected from the group consisting of 4-aminobenzo[b]pyrylium and 4- aminobenzo [b] thiapyrylium salts, said photoconductor being selected from the group consisting of a Group IIIa organo-metallic compound having at least one aminoaryl radical attached to a Group IIIa metal, a Group IVa organo-metallic compound having at least one aminoaryl radical attached to a Group IVa metal and a Group Va organo-metallic compound having at least one aminoaryl radical attached to a Group Va metal.

6. An electrophotographic element as in claim 5 wherein the 4-aminobenzo[ b]pyrylium and 4-aminobenzo[b] thiapyrylium salts have the formula:

wherein:

X is selected from the group consisting of a sulfur atom and an oxygen atom;

Z is an anion;

R is selected from the group consisting of an alkyl radical and an aryl radical;

R is selected from the group consisting of a hydrogen atom, a lower alkyl radical and a lower alkoxy radical; and

R and R when taken separately each represents a hydrogen atom, and when taken together are attached to adjacent carbon atoms and represent the atoms necessary to form a fused aromatic ring.

7. An electrophotographic element as in claim 5 Wherein the 4-aminobenzo[b]pyrylium and 4-a1ninobenzo[b] thiapyrylium salts are selected from the group consisting of:

4-benzylamino-2-phenylbenzo[b]pyrylium perchlorate,

4 anilino 2 (4 methoxyphenyl)naphtho[1,2-b]

pyrylium perchlorate,

1 (N butylamino) 3 phenylnaphtho[2,l-b]

pyrylium perchlorate,

4 (N butylamino) 2 (4 methoxyphenyl)naphtho 1 ,2-b] pyrylium perchlorate, 1-anilino-3-phenylnaphtho[ 1,2-b] pyrylium perchlorate,

4 (N butylamino) 2 phenylbenzo [b]thiapyrylium perchlorate,

4-anilino fiavylium perchlorate,

4 cyclohexylamino 2 phenylbenzo [b]thiapyrylium perchlorate,

4 (N octylamino) 2 phenylbenzo [b]thiapyrylium perchlorate,

4 phenylamino 2 phenylbenzo[b]thiapyrylium perchlorate,

2 phenyl 4 phenethylaminobenzo[b]thiapyrylium perchlorate,

4 (N butylamino) 2 (p methoxyphenyl)benzo- [b]pyrylium fluoroborate, 4 (N butylamino) 2 (p methoxyphenyl)benzo- [b]pyrylium perchlorate,

4 (N n butylamino) 2 (4 methoxyphenyl) benzo[b]pyrylium fiuoroborate, and

4 benzylamino 2 phenylbenzo [b] thiapyrylium perchlorate.

8. An electrophotographic element as in claim 5 wherein the support is electrically conducting.

9. An electrophotographic element as in claim 5 wherein the organo-metallic photoconductor is selected from the group consisting of:

triphenyl-p-diethylaminophenylsilane,

methyl-diphenyl-p-diethylaminophenylsilane, triphenyl-p-diethylarninophenylgermane, triphenyl-p-dimethylaminophenylstannane, triphenyl-p-diethylaminophenylstannane,

diphenyl-bis- (p-diethylaminophenyl) stannane,

triphenyl-p-diethylarninophenylplumbane,

tetra-p-diethylaminophenylplumbane, tetra-p-diethylaminophenylgermane, phenyl-bis-(p-diethylaminophenyl)phosphine,

bis (p-diethylaminophenyl) phosphine oxide,

tris-p-dimethylaminophenylarsine,

tris-p-diethylaminophenylarsine, 2-methyl-4-dimethylaminophenylarsine oxide, tris-p-diethylaminophenylbismuthine,

methyl-bis- (p-diethylaminophenyl) arsine,

1 5 methyl-bisp-diethyl am inophenyl) phosphine, diphenyl-p-diethylaminophenylsilane, p-diethylaminophenylarsine, 4,4',4"-tris diethylamino tetraphenylstannane, tetrakis [diphenyl (p diethylaminophenyl)plumbyl] methane, tetrakis [diphenyl (p diethylarninophenyl)stannyl] stannane, bis- [phenyl- (p-diethylarninophenyl) ]dibisrnuthine, tris-(p-diethylaminophenyl)phosphine sulfide, bis-(p-diethylaminophenyl)thioxostannane, bis [2-mesity-4- (N-piperidino phenyl] borane, bis [2-mesity-4- (N,N-dimethylarnino phenyl] borane, tri-p-diethylaminophenylborane, tri-p-diphenylaminophenylborane, tri-p-methylaminophenylgallium, methyl-phenyl-p-diethylaminophenylborane, 2-naphthyl-p-dimethylaminophenylborane, p-dipropylarninophenylborane, di-p-diethylaminophenylborane, ethoxy-p-dimethylaminophenyl aluminum hydride, diphenoxy-p-dibutylaminophenyl aluminum, tri-( 2,6-dimethyl-4-diethylaminophenyl) indium, 2-chloro-4-dimethylaminophenyl gallium hydride, tri-(2,6-diphenoXy-4-diethylaminophenyl)thallium, tri- (2,6-dimethoxy-4-dimethylaminophenyl) thallium, diphenylamino-p-diethylaminophenylborane, dimesityl-4-dimethylaminonaphthylborane,

1 6 dimesityl-4-dimethylarninophenylborane, dimesityl- 3 ,5-dimethyl-4-methoxyphenyl borane, dimesityl-4-diphenylaminophenylborane, 1,2-bis (p-diethylaminophenyl) diborane, and 1-pheny1-2-methyldiborane.

5 10. An electrophotographic element as described in claim 5 wherein the organo-rnetallic photoconductor is, selected from the group consisting of:

4,4,4"-tris diethylamino) tetraphenylstannane, 10 tetra-p-diethylaminophenylgermane,

4,4-bis diethylamirio triphenylarsine, bis 2-mesityl-4- (N-piperidino phenyl] borane, and bis [2-mesityl-4- (N,N-dimethylamino phenyl] borane.

15 References Cited UNITED STATES PATENTS 2,779,738 1/1957 McBride 260448.2X 3,114,633 12/1963 Schlesinger 96 1.6 3,163,530 12/1964 Schlesinger 9'6-1.6 3,250,615 5/1966 Van Allan et a1. 96-1 3,314,975 4/1967 Jurd 260345.2 3,344,070 9/1967 Schiefer et a1. 260-448.2X

CHARLES E. VAN HORN, Primary Examiner 25 U.S. Cl. X.R. 

